Canon's 1Ds series of cameras exists in a class of its own. With pixel counts well above anything else offered in a 35mm-format digital SLR, an attention to detail that addresses the needs of high-end professionals, and a price tag that's thousands of dollars more than the nearest competition, it continues to push the limits of digital photography. The 1Ds Mark III, the latest in the series, brings the megapixel count to a whopping 21.1 and is every bit a precision instrument. It offers a high level of control over all aspects of your images, a body design that gives you fast access to these controls, and can be customized to tailor certain buttons and functions to your shooting style. It's been over three years since its predecessor was announced, so there are a fair number of new features in the Mark III, which bring it up to date with the latest trends in dSLRs. With this latest model, Canon has stepped up to a pixel count that, up till now, was solely the realm of medium format digital backs, while maintaining an edge in terms of physical size and sharpness of available lenses.

Design
Canon's 1Ds series body design, with its long, relatively straight grip, seems somewhat blocky compared with the sculpted designs that Nikon and some other manufacturers use. However, that's partly because the grip itself is longer, with about 3.25 inches of main grip space compared with the Nikon D3, which has about 2.5 inches of main grip space. That means that the Canon might better accommodate people with larger hands.

Both cameras have longer vertical grips. Speaking of which, as in previous models, Canon duplicates the buttons and dials around the shutter button on the vertical grip, though they omit the exposure compensation and ISO buttons. Since you can use the large control wheel on the camera back for exposure compensation, only the lack of the ISO button is annoying, especially if you've come to rely on it as much as I have recently. To Canon's credit, in my field tests I found that the vertical grip's shutter on the 1Ds Mark III was less prone to accidental pressing than the one on the Nikon D3. Both offer an on/off switch to prevent such accidents when using the main grip.

With its upgrade to a 3-inch LCD screen, from the 1Ds Mark II's 2-inch screen, Canon was forced to relocate some buttons that used to reside to the left of the LCD. Menu and Info buttons move above the screen, while the playback button drops to below it. The Select button from the Mark II N is now obsolete, thanks to the Mark III's Set button, which is mounted in the middle of the large scroll wheel, much like the scroll wheels found on the EOS 40D and 5D. Another feature drawn from those siblings is the tiny joystick controller, which is used to navigate between various menus, among other things.

While the Mark II had three two-button combinations of the buttons to the left of the pentaprism, Canon eliminated two of those combos by including the aforementioned dedicated ISO button and putting both AF and Drive under the same button. The small scroll wheel near the shutter controls one while the large back scroll wheel adjusts the other. The only remaining combo controls bracketing. The very observant among you may notice that Canon now hides the diopter wheel behind the viewfinder's eyecup, so that you now have to remove the eyecup to adjust it. That's good, since you really shouldn't need to change it that often and don't want it to change inadvertently. You might also notice that there's no clearly marked white balance button. The FUNC button handles that, but it would've been nice for Canon to mark it. They also moved the white balance shift to the menu only, so the Mark II's WB +/- button is replaced by the AF-On button, which triggers the autofocus and can come in handy if you don't like the standard half-press of the shutter button to activate focus. As you might guess, there are a number of ways you can configure the shutter and AF-On buttons to work together.

The first thing most people say when holding the 1Ds Mark III is that it's heavy, and they're right. At times though, that weight can help steady your shot and once you get used to shooting with a body that's nearly 3 pounds without a lens attached (but with the battery), the weight isn't as big of an issue, though your arm will feel more tired at the end of a long day of shooting than it would if you were using the 5D. Also, your back may feel it if you carry this camera and a few big pro lenses around for a while.

The 1Ds Mark III's viewfinder offers 100 percent coverage, according to Canon, and in my field tests, it seems like they're at least extremely close, making it joy to frame images, since you're not guessing if what you see through the lens is all of what you'll get. Compared with cameras with smaller sensors, the finder's 0.76x magnification won't look all that impressive, though it's plenty big and bright. If you don't enjoy the screen that comes with the camera, Canon also offers a choice of 15 optional focusing screens to which you can switch. I had no trouble focusing manually with the default screen.

Like the 1D Mark III, the hot shoe on the 1Ds Mark III has a raised hard plastic ridge around the hot shoe that mates with a rubber gasket around the connector on the 580 EX II Speedlight, to seal one of the few spots on the camera that isn't protected by rubber gaskets built into the body already. The shutter is said to last for up to 300,000 cycles, which is a notable increase over its predecessor and puts it even with the shutter in the Nikon D3.

Features
The feature everyone will mention first about the 1Ds Mark III is its 21.1-megapixel Canon CMOS sensor. I wouldn't be surprised if that is followed by a small discussion of the camera's 14-bit per channel analog to digital conversion, which theoretically allows for 16,384 levels of brightness compared to 4,096 levels with the 12-bit Mark II when shooting RAW. Nikon's D3 also offers 14-bit RAW output, but also gives the option to roll that back to 12-bit if you're trying to keep file sizes down. You can't dial down to 12 bit on the Canon, so if you shoot RAW, expect files in excess of 30MB each. Full-size, finest-quality JPEGs can approach 15MB.

Since the sensor's size is the same as a frame of 35mm film (often referred to as full-frame), you don't have to worry about any conversion factors to figure out the "equivalent" field of view that you'll get with any of Canon's EF lenses. However, you won't be able to use any of the company's EF-S lenses. While this bothers some folk, especially because Nikon lets you mount its digital-only DX lenses on its full-frame D3, Canon's EF-S lenses extend further into the body, so the large mirrors on its full-frame and 1.3x focal-length-multiplier 1D series cause a physical conflict. So, Canon's not likely to change this. However, it's typically understood that anyone buying a full frame Canon would know that you can't use EF-S lenses, since the company has been very upfront about this issue from the get go. Also, I should note that the ability to use DX lenses on the D3 comes at the expense of precious pixels.

Outdoor photographers will appreciate the 1Ds Mark III's dust reduction system. It shakes the sensor whenever you turn the camera on or off to shake dust from the IR-cut filter in front of the sensor. That filter is also has an antistatic coating to prevent dust from adhering in the first place. If you end up with any persistent marks on the sensor you can have the camera map the sensor and plot their locations, so you can remove them automatically with the included Digital Photo Professional software.

Following the current trend, the 1Ds Mark III includes a Live View shooting mode, which lets you frame images with the big 3-inch LCD on the back of the camera instead of the optical viewfinder, should you choose to do so. Once the Live View mode is enabled in the setup menu, all you have to do is press the Set button to enter Live View mode. When you do, the camera locks the mirror up, thereby cutting off the optical viewfinder, and you are restricted to manual focus. If you're worried about light leaking in through the viewfinder, you can block it with the built-in eyepiece shutter by flipping down the switch in the right side of the viewfinder. Conveniently, you can use the playback zoom controls to zoom in either 5x or 10x on your subject, to aid in manual focusing. Canon doesn't set any strict limits on how long you can remain in Live View mode, but it does mention that the sensor heats up in Live View mode and that you may encounter a thermometer icon on the LCD once the camera reaches a certain temperature. I never saw this icon when I used Live View mode, but if you typically shoot in very warm environments (studio hot lights, anyone?) you may run into it. As you may guess, shooting at higher ISOs should make the sensor heat up faster than at lower ISOs. Canon also warns that increased temperatures can lead to increased image noise.

Canon has increased the number of cross-type autofocus points from 7 in the Mark II to 19 in the Mark III. Cross-type AF points typically provide a higher level of sensitivity compared to standard horizontal-only points. Those 19 cross sensors are joined by 26 "assist points" for a total of 45 AF points. Careful scrutiny of Canon's manual shows that the number of active cross-type points decreases drastically if you use a lens with a maximum aperture slower than f/2.8. When you step down to a lens with a maximum aperture of f/4, only the center point functions as a cross-type; the rest function as horizontal only. With a maximum aperture of f/5.6, all AF points become horizontal only and by the time you reach a maximum aperture of f/8 you're left with only the center point active and it acts as a horizontal-only sensor. This is essentially the same system that is employed in Canon's 1D Mark III, which still has an ongoing problem with continuous AF under certain conditions, including very hot and bright shooting conditions, according to Rob Galbraith. I saw no such problems in my field tests with the 1Ds Mark III, though I did most of my testing in winter in New York City. Still, there's no real reason to think that the 1Ds Mark III has any such problem in the first place.

To determine a proper exposure, the camera uses a 63-zone TTL (through the lens) metering system. The system offers full-frame evaluative metering, center-weighted average, and partial and spot metering. According to Canon, the partial option uses the center 8.5 percent of the frame to determine exposure, while the spot setting uses 2.4 percent and can be set to the center or linked to the AF sensor in use, or you can choose up to eight spot readings and let the camera average them. Canon calls this last option "multispot metering." All you have to do is press the FEL button to add another spot reading while you're in spot AF mode to begin with. The average of the total number of spots is used, and you can even apply exposure compensation. While it worked well, it took me a little time to figure out that you have to point the active spot at each part of the scene for which you want to add a reading and then recompose before capturing your image. Sure, that makes sense, but the manual probably could've communicated that a little more clearly.